The present invention is related to a direct injection bi-fuel system for a combustion engine that is configured to separately provide fuel from two sources. In particular, the system is a direct injection bi-fuel system configured to separately provide two types of fuel, being liquid fuel and liquefied gas fuel, as desired, to a combustion engine.
Direct injection fuel systems are configured to inject fuel directly into a cylinder of a combustion engine instead of premixing the fuel with air in separate intake ports. This configuration allows for controlling combustion and emissions more precisely, but it demands more advanced engine management technologies. The higher torque provided by modern direct injection gasoline engines is the result of the synergistic effect of direct injection, charging, and variable valve timing. In combination, these aspects of direct injection technology allow for great flexibility in the engine tuning. As a result, there tends to be a superior cylinder charge with a reduced tendency to knock.
In the automotive industries, the direct injection technology for petrol, or gasoline, has already been introduced for several engine types. This means that the common existing liquefied petroleum gas (“LPG”) technology has to be changed or improved or completely redesigned in order to be utilized along with the existing direct injection technology for petrol.
There are at least two options to use LPG for direct injection engines. First, provide indirect LPG injection through port injection, and second, provide direct LPG injection into the burning chamber. The indirect LPG injection system is mainly based on the existing master slave sequential injection that is also used for indirect injection engines. The direct LPG injection system is a new system that is still in development. When using the direct injection technology with LPG, the advantages for environment may be obtained through reduction of carbon dioxide and particles into the atmosphere.
In normal operation, the direct injection combustion engine uses a high pressure fuel pump, high pressure fuel rail, and direct injectors to directly inject the fuel into the combustion chamber. To reduce cost and overall system complexity, it is desirable to use the high pressure components for both types of fuel. To make this possible, the system should be able to replace the first type of fuel with the second type of fuel and vice-versa.
There are physical challenges that may occur when switching between two types of fuel. First, when replacing one fuel with another fuel during engine operation, undesirable mixing can occur. Second, when the system is using liquefied gas fuel as one type of fuel and liquid fuel as the other type of fuel, depending on gas composition and temperature, it is possible that the pressure of the liquefied gas system will operate at a higher pressure than the liquid fuel system.